1. Field Of The Invention
The present invention relates to a process for the control of a space craft performing a precession movement and to an apparatus for the realization thereof. It more particularly relates to the positioning of the upper stage of a launcher prior to the release of payloads (satellites).
The positioning of the upper launcher stage prior to the release of payloads is a crucial problem in space missions, because it conditions the satisfactory placing in orbit of said payloads.
A rapid precession movement (5 r.p.m. or higher) permits a good gyroscopic stabilization of a payload during its travel between the release orbit and its operating orbit. During this travel, a released payload without a precession movement and only having a limited transverse velocity, will deviate from its nominal direction. This deviation must be made good by a putting into operation of the jet pipes or nozzles, which results in a significant energy loss, which reduces the life of the satellite, which is intimately linked with its fuel reserves.
The application of a parasitic transverse velocity to a payload performing a precession movement does not modify its general orientation. The payload only has a rotational movement in accordance with a cone directed around the general orientation axis. Thus, it is merely necessary at the release of the payload for said orientation axis to be close to the nominal direction in order to retain this precision throughout the orbit transfer and without using an active check for putting the nozzles into operation. Thus, significant energy savings result.
FIGS. 1a to 1f show a known sequence of operations for the successive release of two payloads. FIG. 1a shows the upper stage 10 of the launcher and two payloads 12, 14. Payload 12 has been released and is moving away from the stage 10. Payload 14 is still contained in the protecting Spelda or Sylda-type structure 16.
Arrows 18 and 20 indicate the precession movements of the upper stage 10 and the payload 12 about the longitudinal axis Xl. Following the release of the first payload 12, during a second stage shown in FIG. 1b, the precession movement of the upper stage is stopped. During the following stage shown in FIG. 1c, the upper part 16a of the Spelda is ejected revealing the second payload 14 contained in the lower part 16b of the Spelda.
The upper stage 10 is then tilted into the release position for the second payload 14. This operation is shown in FIG. 1d, where the arrow 22 symbolizes the tilt.
FIG. 1e shows the placing in precession of the upper stage 10 symbolized by the arrow 24. FIG. 1f diagrammatically shows the release of the second payload 14 performing a precession movement symbolized by the arrow 26.
FIGS. 1a to 1f show six nozzles 1 to 6 distributed in the form of two sets of three nozzles positioned on the stage 10 so as to supply rotational movements in the pitch-yaw plane (in order to obtain precession movements), as well as those necessary for the tilting.
Conventionally, the positioning of the stage 10 takes place when the latter is stabilized, i.e. without a precession movement and the precession movement is then imposed thereon. No checking with respect to the orientation of the longitudinal axis Xl of the upper stage 10 is carried out following its placing in precession. The direction of the axis Xl during the release of the payload can be subject to error inter alia due to the dynamic unbalance of the assembly formed by the launcher and the payload or nozzle installation errors. Therefore this error must be made good, which involves considerable energy losses prejudicial to the long life of the payload. This type of release is normally called open loop spin release.